I have two Windows Server 2008 SP2 machines (TFS and TFSBUILD). Periodically, the TFSBUILD server shares (\TFSBUILD\ShareName or \TFSBUILD\C$) become unresponsive to requests from Windows Vista (Server 2008) and Windows 7 client requests. Windows XP machines are still able to connect.

No events in the server log indicate any problem. A simple restart corrects the issue temporarily, but it always returns.

There seems to be a somewhat related question here. One answer that sticks out is to check the "File and printer Sharing for Microsoft Networks" option on the network adapters. However, this would likely cause it to never work, not stop working after a while.

I'd suggest you get Wireshark on the server and start a trace of the network traffic. Check to see what it looks like when XP clients connect to a share, and when the Win7/Vista clients connect (both when it works and after it stops working). Hopefully you'll find some obvious missing piece when it's not working that can help lead to the actual cause.